Don't crash while detaching a pending child frame under --site-per-process.

content/browser/frame_host/render_frame_host_manager.h

Index: content/browser/frame_host/render_frame_host_manager.h
diff --git a/content/browser/frame_host/render_frame_host_manager.h b/content/browser/frame_host/render_frame_host_manager.h
index 4d60c0eede89664e8fea23bf2c2b9975e2991c95..043b0a982d3d73542d4116bd91e45ba2648ad43b 100644
--- a/content/browser/frame_host/render_frame_host_manager.h
+++ b/content/browser/frame_host/render_frame_host_manager.h
@@ -507,9 +507,13 @@ class CONTENT_EXPORT RenderFrameHostManager : public NotificationObserver {
   // swapped out.
   void ShutdownRenderFrameProxyHostsInSiteInstance(int32 site_instance_id);
 
-  // Helper method to terminate the pending RenderViewHost.
+  // Helper method to terminate the pending RenderFrameHost. The frame may be
+  // deleted immediately, or it may be kept around in hopes of later reuse.
   void CancelPending();
 
+  // Clears pending_render_frame_host_, returning it to the caller for disposal.
+  scoped_ptr<RenderFrameHostImpl> UnsetPendingRenderFrameHost();
+
   // Helper method to set the active RenderFrameHost. Returns the old
   // RenderFrameHost and updates counts.
   scoped_ptr<RenderFrameHostImpl> SetRenderFrameHost(